Manatees and seagrass brought some of land's evolutionary advances into the sea.
AURORA PHOTOS/ALAMY STOCK PHOTO
By Elizabeth Pennisi
Life probably originated in water, but nature did some of its best work once organisms made landfall. That’s what Geerat Vermeij has concluded after surveying fossils and family trees to discover where and when some of life’s greatest modern advances evolved.
Almost all of these seemingly out-of-the-blue innovations, from fungus farming by insects to the water transport systems that made tall trees possible, came about after plants and animals learned how to survive on land some 440 million years ago, Vermeij, an evolutionary biologist at the University of California, Davis, reported last week in Current Biology.
“The idea that a dramatic ‘pivot’ in the locus and tempo of biological innovation occurred once complex life colonized the land surface is quite profound,” says Stefan Lalonde, a geobiologist at the European Institute for Marine Studies in Plouzané, France.
Many researchers have focused on how newly land-based organisms coped with gravity and the threat of desiccation. But Vermeij wondered instead how the move to land might have changed the pace of evolution.
He compiled a list of key innovations that showed up in several groups of organisms and provided a big competitive edge, such as herbivory by vertebrates, flight, echolocation, and warm-bloodedness. Existing fossil evidence enabled him to date the origin of a dozen of these adaptations.
Nine appeared first on land and later in the sea, he reported. “Once they evolved on land, they could re-enter the oceans,” where they had a big effect on the ecosystems there, comments Nick Lane, a biochemist at University College London. For example, seagrasses brought land plants’ systems for transporting water and acquiring nutrients back to the marine environment. Vermeij found two other traits that are still restricted to land. Another, the tendency of animals to guard their plant or plantlike food sources—appeared about 50 million years ago in both places. Just one, the ability to use electrical currents for communication and hunting—think electric eels—happened first, and only, in water.
Lalonde, too, has found evidence of differences in evolution on land and in the sea by studying land-based and sea-going microbes that produced oxygen billions of years ago.
But he and some others are not convinced that Vermeij has found a real pattern. “A major difficulty is avoiding bias in the selection of the set of major innovations,” Lalonde says. Many innovations, such as long-distance migration and color vision, don’t show up in the fossil record and so were not counted.
Still, the work “will encourage us to think about whether there is something special about the terrestrial environment,” says Charles Delwiche, an evolutionary biologist at the University of Maryland in College Park. Vermeij thinks life on land was less constrained because air is easier to move around in than water, but Charles Wellman, a paleontologist at the University of Sheffield in the United Kingdom, wonders whether the terrestrial environment was more stressful, forcing organisms to innovate to survive. And Delwiche suggests that the availability of new places to live was what fueled the surge of innovation following the conquest of the land.
“I don’t know if I believe” the article, Delwiche says. “But the thing that I love about it is it gets me thinking.”
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